Breathing apparatus

ABSTRACT

A breathing apparatus of the type having a rebreathing system from which the user inhales and into which he exhales and which receives fresh gas making up for consumed oxygen. The rebreathing system alternately operates as a fully closed system and a fully open system; it operates in the closed mode during a series of breaths until the oxygen in the system has been consumed, and then it operates in the open mode to permit exhalation to the ambient medium. The switching of the system between the open and closed modes is effected in dependence on the volume of gas inhaled, or the number of inhalations made, during the course of the series of breaths, and the volume of gas exhaled, or the number of exhalations, to the ambient medium.

Unite States atent Lundgren et a1.

[ BREATHING APPARATUS [75] Inventors: Claes E. G. Lundgren, Lund; Stig L.

Akesson, Malmo, both of Sweden [73] Assignee: AGA Aktiebolag, Lidingo, Sweden [22] Filed: Aug. 20, 1971 21 Appl. No.: 173,605

[30] Foreign Application Priority Data Aug. 24, 1970 Sweden 11489/70 [52] US. Cl. 128/1422 [51] int. Cl B63c 9/00, A61m 16/00 [58] Field of Search 128/142, 142.2, 142.3, 128/191 R, 188, 145.8, 145.6, 145.5, 202

[56] References Cited UNITED STATES PATENTS 2,931,357 4/1960 Arborelius 128/191 3,016,053 l/l962 Medouch 128/142 3,292,617 12/1966 McDonough 128/202 3,695,261 10/1972 Emmons 128/1422 Primary ExaminerRichard A. Gaudet Assistant ExaminerG. F. Dunne Attorney, Agent, or Firm-Larson, Taylor & Hines [5 7] ABSTRACT A breathing apparatus of the type having a rebreathing system from which the user inhales and into which he exhales and which receives fresh gas making up for consumed oxygen. The rebreathing system alternately operates as a fully closed system and a fully open system; it operates in the closed mode during a series of breaths until the oxygen in the system has been consumed, and then it operates in the open mode to permit exhalation to the ambient medium. The switching of the system between the open and closed modes is effected in dependence on the volume of gas inhaled, or the number of inhalations made, during the course of the series of breaths, and the volume of gas exhaled, or the .number of exhalations, to the ambient medium.

15 Claims, 10 Drawing Figures PATENTED B 61974 sum 1 0r 5 PAIENIE AUG 5 m4 KHEET 2 OF 5 SHEET 3 [IF 5 Fig. 5

BREATHING APPARATUS This invention relates to breathing apparatus and more particularly to breathing apparatus of the type where the breathing gas is rebreathed several times.

Mixed-gas breathing apparatus for use under water, in smoke or in other environments of normal or elevated pressures where the ambient medium is un breathable are known since many years. A common feature of known apparatus of this type is that fresh gas consisting of oxygen and an inert gas (usually nitrogen or helium) is constantly fed to a rebreathing system, either continuously or in portions on each breath of the user. In use of the apparatus the user inhales from and exhales to this rebreathing system. A portion of the breathing gas is circulated in the system and freed from carbon dioxide while the remainder is exhausted to the ambient medium.

The quantity of gas that is exhausted is determined by the constant feed of fresh gas. The feed of fresh gas has to be sufficient to meet the oxygen demand of the user during periods of hard work and still prevent an undue decrease of the oxygen partial pressure. In addition, the fresh-gas feed must by controlled such that during periods of low oxygen consumption the'oxygen partial pressure does not rise to a level where oxygen poisoning may be likely to occur.

The rate of oxygen consumption of a human being varies such that during hard work the rate of oxygen consumption is about six times the rate of oxygen consumption during rest. Thus, mixed-gas breathing apparatus of the above-mentioned known type wastes considerable amounts of the breathing gas during periods of low oxygen consumption, and an oxygen content of the fresh gas which is sufficient for periods of high oxygen consumption may be too high for periods of low oxygen consumption.

Variation of the oxygen content causes variation of the inert-gas content with attendant difficulties of determining the latter. This makes it difficult to make accurate decompression or ascent tables; if the inert-gas content is underestimated, a risk of decompression sickness arises, and if the inert gas content is overestimated, the ascent times become unduly long.

As mentioned above, known mixed-gas breathing apparatus causes considerable wastage of the breathing gas, particularly during periods of low rates of oxygen consumption. This means that the gas supply is inefficiently utilized, or, in other words, that the user has to carry a large supply of gas in order that long operation times (the maximum times the user can safely remain under water or in the unbreathable atmosphere) may be possible.

An object of the invention is to provide means permitting control of the partial pressures of the oxygen and the inert gas; an accurate control of these partial pressures facilitates avoiding oxygen poisoning, oxygen deficiency and decompression sickness and also makes possible an optimum utilization of the gas supply, meaning long operation times and minimum decompression times.

Broadly stated, the invention embodies a breathing apparatus having a rebreathing system from which exhalation to the ambient medium is possible, a fresh-gas supply for feeding fresh gas to the rebreathing system to replace gas that has been consumed and exhausted to the ambient medium, and control means maintaining the rebreathing system in a closed condition with respect to the ambient medium during a series of breaths to and from the rebreathing system and opening the rebreathing system for exhalation to the ambient medium after the termination of the series of breaths.

The invention is based on the following considerations:

Irrespective of the magnitude of the rate of oxygen consumption, and hence the ventilation (that is, the volume of gas that is breathed per unit of time), the ratio of the volume of gas rebreathed to the rebreathing system to the volume of gas exhausted to the ambient medium is caused to assume a given value. This is accomplished in that on each of a series of consecutive breaths the exhaled gas is returned through a carbon dioxide filter to a breathing bag or other storage container from which it is inhaled on the next breath; thus, during the series of breaths the rebreathing system operates as a fully closed system. After the series of breaths a valve system is actuated such that exhalation to the ambient medium takes place; in order that the best result may be achieved, this exhalation to the ambient medium continues until the total exhaled volume has a given controlled ratio the total volume that has been exhaled to the storage container during the series of breaths. This ratio is automatically controlled in such a manner that a relatively larger proportion is exhaled to the storage container at greater depths. Replenishment of the system with fresh breathing gas is made from a fresh-gas supply which is automatically opened after the exhalation to the ambient medium.

Physiologically the breathing of human beings is such that independently of the metabolism, and hence the rate of oxygen consumption, and of the total pressure of the breathing gas, each breath reduces the oxygen content of the breathing gas an amount equivalent to a reduction of the oxygen partial pressure by about 0.05 atm. (atmospheres). In order that oxygen poisoning may be avoided, the average partial pressure of the oxygen of the breathing gas should not exceed 15 atm. absolute, and the initial partial pressure should not exceed 2 to 2.5 atm. absolute, depending on the duration of the series of breaths to and from the storage container; the initial partial pressure should be lower for longer durations. In order that oxygen deficiency may be avoided, the oxygen partial pressure should not be below 0.2 atm. absolute.

It is well-known that the frequency and depth of the breaths may vary considerably from one individual to another even for equal oxygen consumptions and ventilations. It follows from this fact that the absorption of oxygen from the volume of gas inhaled on each breath may vary. For that reason, a prerequisite for an accurate control of the partial pressures of oxygen and inert gas is a device which is controlled by the total volume of gas rebreathed (the total saved volume) to the storage container during the series of breaths (one breathing cycle).

The advantages achieved by the invention are shown by the following example in which the physiological data given above are applied and the supply of fresh gas is assumed to contain one cubic meter of gas consisting of 30 percent oxygen and percent inert gas.

1. OPERATION TIMES The operation times of the apparatus according to the invention are compared with the operation times of conventional breathing apparatus having a fully open breathing system, that is, apparatus in which the inhalation is from the fresh-gas supply and the exhalation is to the ambient medium, and of conventional mixed-gas breathing apparatus, that is, breathing apparatus in which there is a constant supply of fresh gas to a rebreathing system containing a carbon dioxide filter.

The comparison is made for two rates of oxygen consumption, namely, one low, 0.8 liters per minute, and one high, 3.0 liters per minute. Moreover, the comparison is made for diving to two water depths, namely 20 meters (corresponding to an ambient pressure of 3 atm. absolute) and 50 meters (corresponding to an ambient pressure of 6 atm. absolute).

The following table permits a comparison of the operation times of the various systems.

Operation times in hours 2. PARTlAL PRESSURES OF OXYGEN AND INERT GAS The rate of oxygen consumption is assumed to be 1 liter per minute and the diving depth is assumed to be 20 meters. To show the importance of controlling the saving and waste of breaths (that is, the exhalation to the storage container and to the ambient medium, respectively) in dependence on the total volume of gas exhaled into the storage container during a breathing cycle, it is assumed that this rate of oxygen consumption is met by, in one case, twenty breaths per minute with each breath having a volume of 1.0 liter, and in another case, ten breaths per minute with each breath having a volume of 2.0 liters. Moreover, it is assumed that a fresh-gas volume of 2.0 liters is available in the system.

In the first case a quantity of 0.05 liters of oxygen is absorbed from each breath. Distributed among the available 2 liters of fresh gas, the attendant reduction of the oxygen partial pressure is 0.025 atm. The oxygen partial pressure of the fresh gas initially is 0.9 atm. absolute (since, according to the assumptions made, the ambient pressure is 3 atm. absolute, and the oxygen content 30 percent) and can be reduced to 0.2 atm. absolute. Accordingly, the available volume of fresh gas can be used for (O.9O.2)/0.025 28 breaths. In the second case a quantity of 0. 1 liter of oxygen is absorbed from each breath, meaning a reduction of the oxygen partial pressure in the system by 0.05 atm. In this case the available volume of fresh gas can be used for 14 breaths. v

Because the breathing apparatus is controlled by the total rebreathed volume, exhaustion to the ambient medium will take place after 28 breaths in the first case and 14 breaths in the other case when, in both cases, a gas volume of 28 liters has been breathed. Rebreathing takes place during a period of L4 minutes (28 breaths at 20 breaths per minute and 14 breaths at 10 breaths per minute, respectively) at the given rate of oxygen consumption.

The exhaustion to the ambient medium that takes place after each series of breaths is effected by as many exhalations as are required to provide space for a new charge 2 liters in the example above of fresh gas.

In both cases the initial oxygen partial pressure is 0.9 atm. absolute, and the final oxygen partial pressure is 0.2 atm. absolute, during each breathing cycle comprising the series of breaths to and from the storage container. Thus, the average oxygen partial pressure is 0.55 atm. absolute, and it is independent of the rate of oxygen consumption and the frequency of the breaths. The average partial pressure of the inert gas is 30.55 2.45 atm. absolute. This value can be used for calculation of the decompression times.

Obviously, the above discussion is simplified. The lungs of the user as well as the breathing apparatus have some residual volumes even when emptied which should be taken into account when the partial pressures are calculated. Unlike the breathed volumes, however, these residual volumes are fairly constant, and for that reason they have no significant bearing on the fundamental reasoning above.

In the above example the depth is assumed to be 20 meters. If the depth is 30 meters, for example, the initial oxygen partial pressure is increased from 0.9 to 1.2 atm. absolute, resulting in a corresponding increase of the operation time. Accordingly, for optimum utilization of the breathing gas, the number of breaths to and from the storage container during each breathing cycle should be increased with increasing ambient pressure. The volume exhaled during the exhaustion, however, should be independent of the depth. Accordingly, for increased depths the ratio of the rebreathed (saved) volume of gas to the exhausted (wasted) volume of gas is increased.

The operation times are determined by the difference between the initialand final oxygen partial pressures. lncreased oxygen content of the fresh gas increases the operation times. A limit is set by the danger of oxygen poisoning, and this danger in turn is dependent on the average oxygen partial pressure during a breathing cycle. The decompression time is determined by the average value of the partial pressure of the inert gas and this value should be kept as low as possible to permit an efficient utilization of the breathing gas and the apparatus.

From the above it is seen that the oxygen partial pressure of the fresh gas should be as high as possible. By maintaining a high oxygen content of the fresh gas when the ambient pressure is low and decreasing the oxygen content with increasing ambient pressure, it is possible to increase the operation time and decrease the decompression times.

Preferred embodiments of the invention are described in the following detailed description and diagrammatically illustrated in the accompanying drawings, in which:

FIG. 1 is a diagrammatic representation of a breathing apparatus embodying the invention;

FIGS. 2 and 3 are diagrammatic representations of alternative embodiments of the fresh-gas supply of the apparatus shown in FIG. 1;

FIG. 4 shows a modification of an element of the embodiment shown in FIG. 3;

FIGS. 5 to 7 show an embodiment of the breathing system of the apparatus shown in FIG. 1, FIGS. 6 and 7 being sectional views on lines VIVI and VII-VII, respectively, of FIG. 5;

FIG. 8 shows another embodiment of the breathing system of the apparatus shown in FIG. 1;

FIGS. 9 and are diagrammatic representations of modifications of the breathing apparatus shown in FIG. 1.

For simplicity of illustration, simple symbols are used in the drawings to represent several components of the apparatus according to the invention. It will be understood, however, that unless otherwise stated these components are conventional and of a type which is well known in the art.

The breathing apparatus diagrammatically shown in FIG. 1 comprises a rebreathing or circulating system which is generally designated 1. The user inhales from and exhales to this rebreathing system through a mouthpiece 2 having means for ensuring a unidirectional flow of the breathed gas as shown by arrows. The rebreathing system includes a storage container 3 which is exposed to the ambient pressure and which changes its volume with small pressure losses in response to each inhalation of exhalation. Thus, its volume increases on exhalation and decreases on inhalation. The storage container includes a mechanism 4 for mechanically actuating a valve 5 which feeds metered amounts of breathing gas, namely, a mixture of oxygen and an inert gas, such as nitrogen or helium, to the rebreathing system from a fresh-gas supply 6 having means for regulating the supply. Such feeding may take place in response to a very deep inhalation, in response to the using up of the fresh gas in the system, or in response to an increase of the ambient pressure. The rebreathing system also includes a filter 7 absorbing the carbon dioxide of the exhaled gas, and a'relief valve 8 preventing overpressure in the storage container and consequent exposure of the respiratory system of the user to excess pressure.

So far as it has been described above, the breathing apparatus is known. According to the present invention it is supplemented in the following manner in order to yield the aforementioned advantages as regards the reliability of the metered supply of gas to the user and the optimum utilization of the fresh gas:

1. The rebreathing system 1 is provided with a valve 9 which, in one position, permits the exhaled gas to pass freely through it and circulate in the rebreathing system and, in another position, opens the rebreathing system for exhalation to the ambient medium and blocks the circulation in the system. As will be described in more detail hereinafter, this valve may be controlled in one of the following manners:

a. The total volume of gas exhaled to the rebreathing system during one breathing cycle comprising a series of breaths in the rebreathing system controls the setting of the valve 9 to the position in which exhalation to the ambient medium takes place and the total volume of gas exhaled to the ambient medium controls resetting of the valve 9 to the position in which exhalation to the rebreathing system takes place.

b. The number of exhalations to the rebreathing system during one breathing cycle controls setting of the valve 9 to the position in which exhalation to the ambient medium takes place and the number of exhalations to the ambient medium controls resetting of the valve 9 to the position in which exhalation to the rebreathing system takes place.

0. The control is effected in the manner set forth under a) or b) supplemented with automatic adjustment of the rebreathing time, that is the time during which exhalation to the rebreathing system takes place, in dependence on variations of the ambient pressure.

2. The fresh-gas supply 6 embodies one of the following systems:

a. A supply system according to FIG. 2 which is known in connection with air breathing apparatus and comprises a high-pressure supply bottle 10 for fresh gas of a constant composition, a main shut-off valve 11, a pressure gage 12 indicating the supply pressure, a warning or reserve gas valve 13 which functions when the gas supply pressure has been reduced to a predetermined value to call the attention of the diver to that fact, a pressure regulating valve 14, and a branch conduit including a check valve 15 for supplying fresh gas from another source.

b. A supply system of the type known from US. Pat. No. 3,429,326 for supplying a mixture of two gases of adjustable ratio of mixture. The system is adapted as shown in FIG. 3 to the needs of the present case. This supply system includes a supply bottle 16 containing oxygen, a supply bottle 17 containing inert gas or a mixture of oxygen and inert gas, main shutoff valves 18 and 19, supply pressure gages 20 and 21, a warning or reserve gas valve 22 functioning when the oxygen supply pressure has dropped to a predetermined value, pressure regulating valves 23 and 24, branch conduits including check valves 25 and 26 for supplying gas from another source, a controlled regulating valve 27 in the oxygen circuit, an oxygen shut-off valve 28 controlled from the output conduit by way of a sensing conduit 29, a restriction 30, a control conduit 31 employed for the control of the supply of gas from the bottle 17, a pressure regulating valve 32, fixed restrictions 33 and 34 for the flows of the two gases, a variable restriction 35 by means of which different mixture ratios may be selected, and an indicator 36 showing the selected mixture ratio.

c. A supply system as set forth under b) where the variable restriction 35 of FIG. 3 is replaced by a known valve device as shown in FIG. 4 so that the adjustment of the mixture ratio is effected automatically. In this valve device a closed aneroid box or bellows 37 actuates a valve 38 such that the valve is fully, or almost fully, open at low ambient pressures and gradually closed when the ambient pressure increases so that the oxygen content of the gas mixture is reduced with increasing ambient pressure.

FIGS. 5 to 7 show an embodiment operating in accordance with items 1a and 2a above. In these figures, 39 is a storage container in the form of a bellows-type breathing bag, 40 is a carbon dioxide filter, 41 is a mouthpiece, 42 is a springloaded exhalation valve for exhalation to the ambient medium, 43 is a springloaded inhalation valve, 44 is a spring-loaded exhalation valve for exhalation to the breathing bag, and 45 is a replenishment valve for admitting pressurized gas from a fresh-gas supply 46 into the breathing bag. In response to inhalation through the mouthpiece 41 and the inhalation valve 43, the volumetric capacity of the breathing bag 39 is reduced. As a consequence, a pivotally mounted rigid wall 47 of the breathing bag is pivoted about an axis 48 and, via a friction clutch 49, swings a lever 50 downwardly, as seen in FIGS. 6 and 7. A pawl 51 mounted on the lever 50 then rotates a uniformly toothed ratchet wheel 52 in a forward direction a number of teeth proportional to the reduction of the volumetric capacity of the breathing bag, whereupon another pawl 53 locks the ratchet wheel 52 against rotation in the opposite, or backward, direction. Upon the exhalation, the exhaled gas passes through the filter 40 and opens the exhalation valve 44 against the influence of a spring 54, a stem 55 of the valve 44 moving through one of a number of slots 56 of the ratchet wheel 52. The spring bias on the exhalation valve 42 is stronger than that on the exhalation valve 44, and consequently the former remains closed. The breathing bag 39 thus receives the exhaled gas. After the ratchet wheel 52, which functions as an integrating flow meter, has been rotated in the forward direction a predetermined number of times, as determined by the length of the slots 56, the exhalation valve 44 is maintained in closed position when the next exhalation occurs, in that the valve stem 55 engages one of the lands between the slots 56 of the ratchet wheel 52. The exhaled gas therefore is caused to flow through the other exhalation valve 42 to the ambient medium. During a subsequent inhalation the valve 45 is actuated mechanically by the pivoted wall 47 to admit fresh gas into the breathing bag. By varying the relative lengths of the slots 56 of the ratchet wheel 52 and the lands separating the slots, the ratio of the saved or rebreathed volume of gas to the wasted or exhausted volume of gas may be varied to take different gas mixtures and diving depths into account.

The above-described embodiment can readily be made to operate as set forth under items 1b and 2a above by limiting the movement of the lever 50 such that the ratchet wheel 52 is rotated through a constant angle if the pivoted wall 47 is moved past a predetermined position corresponding to a given minimum exhaled valume in response to each breath. This will produce a constant ratio of the number of saved breaths to the number of wasted breaths. The limitation is accomplished by means of a pair of adjustable abutments 57A disposed at the ends of a slot 57 in a wall 57B through which the lever 50 extends, as shown in FIG. 7. In this case the ratchet wheel operates as a breath counter.

An embodiment operating as set forth under items 10 and 2a above is shown in FIG. 8. This embodiment differs essentially from that shown in FIGS. 5 to 7 only in that in the former embodiment the ratchet wheel 52 of the latter embodiment is replaced by two ratchet wheels 58 and 59 fixedly mounted on a common rotable shaft 60. The ratchet wheel 58 is uniformly toothed throughout its circumference while the ratchet wheel 59 is provided with teeth only at two diametrically opposite locations. The lands separating the slots 56 of the ratchet wheel 52 in FIGS. 5 to 7 are replaced by an elongated plate 61 secured to the shaft 60 and having the same angular orientation as the toothed portions of the ratched wheel 59. The ratchet wheel 58 is rotated in the forward direction (counterclockwise, as seen from the right in FIG. 8) together with the ratchet wheel 59 and the plate 61 by a pawl 62 and the ratchet wheel 59 is rotated in the same direction together with the ratchet wheel 58 and the plate 61 by another pawl 63 (pawls corresponding to the pawl 53 of FIGS. 5 to 7 are also provided but omitted for clarity). Since the ratchet wheel 59 is toothed only at two diametrically opposite portions of the circumference having the same angular orientation as the plate 61, the pawl 63 can rotate the ratchet wheel 59 only when the plate 6l prevents the stem of the valve 44 from moving longitudinally to open this valve, that is, when the exhaled air is caused to flow to the ambient medium through the exhalation valve 42; this corresponds to the engagement of the valve stem 55 of FIGS. 5 to 7 with the lands of the ratchet wheel 52.

The ratchet wheels 58 and 59 are rotated in the forward direction by the pawls 62 and 63 upon the compression of the breathing bag 39, the movement of the pawl 63 always corresponding to the movement of a given point on the breathing bag, namely, the point 65 on the pivoted wall 47 where the pawl 63 is pivotally connected to that wall. The movement of the pawl 62 has the same amplitude as that of the pawl 63 only if the ambient medium is at atmospheric pressure. The movement of the pivoted wall 47 of the breathing bag 39 is transmitted to the pawl 62 by way of a push rod 66 and a single-armed lever 67. The push rod 66 is displaced parallel to itself along the lever 67 in dependence of the ambient pressure, that is, the diving depths, by means of a spring-loaded bellows 68 which is expanded and compressed linearly in dependence of the ambient pressure. When the ambient medium is at atmospheric pressure, the push rod 66 is held opposite that point 69 at which the pawl 62 is pivotally connected to the lever 67. This is shown in dashdot lines in FIG. 8. The push rod 66 and the pawl 63 then engage the pivoted wall 47 at equal distances from the pivot axis 48 of the latter; in other words, this axis is parallel to the dash-dot line 70 passing through the point 65 where the pawl 63 is connected and the point where the push rod 66 engage the wall 47. Both pawls 62 and 63 accordingly are moved through equal distances. If the ambient pressure is increased, the bellows 68 is compressed and displaces the push rod 66 in a direction away from the pivot axis of the lever 67 toward the position shown in full lines, and as a result, the movements of the pawl 62 are shortened in dependence of the displacement of the push rod.

With the above-described structure it is ensured firstly that with varying ambient pressure, varying gas volumes will be rebreathed to the breathing bag 39 during the breathing cycle (when the displacement of the valve stem 55 in the valve opening sense is not prevented by the plate 61), and secondly that when exhalation to the ambient medium takes place (when the displacement of the valve stem 55 is prevented), the volume of gas exhaled to the ambient medium is equal for all ambient pressures.

FIGS. 9 and 10 show modifications providing the above-described functions. These modifications will be described only to the extent that they differ from the system shown in FIG. 1.

In the modification shown in FIG. 9, the fresh-gas supply 6 with the supply regulating means is connected to the rebreathing system 1 via a so-called demand valve 71 of the type commonly used in breathing apparatus which is adjusted such that it opens to supply gas in response to a pressure drop greater than that corresponding to emptying the storage container 3. The valve 9 is controlled in the above-described manner but concurrently with the setting of the valve to the position in which exhalation to the ambient medium takes place, a spring or another suitable mechanism is tripped to cause complete emptying of the storage container through the relief valve 8. This arrangement is well known in the art and therefore it is represented merely by a control conduit 72 in FIG. 9.

in FIG. 10 a control conduit 73 is provided which causes replenishment of the storage container 3 while the valve 9 is in the position at which exhalation to the ambient medium takes place. The replenishment continues until a predetermined pressure within, or a predetermined condition of, the storage container 3 has been reached; this is effected by means which are well known in the art.

What is claimed is:

1. Breathing apparatus comprising a rebreathing system having exhalation valve means through which exhalation to the ambient medium is possible, a variable volume storage container in said system for breathing gas, a fresh-gas supply means for feeding fresh breathing gas from said supply directly into the rebreathing system in response to a predetermined reduction of the volume of the storage container to replace breathing gas that has been consumed and exhausted to the ambient medium, and control means operating independently of time for maintaining the exhalation valve means of the rebreathing system in closed condition with respect to the ambient medium in the course of a series of breaths to and from the rebreathing system and automatically opening the exhalation valve means of the rebreathing system for exhalation to the ambient medium after the termination of said series of breaths, and thereafter automatically closing the exhalation valve to return the rebreathing system to said closed condition.

2. Breathing apparatus as set forth in claim 1, in which the control means include time-independent means for effecting the opening of the rebreathing system for exhalation to the ambient medium automatically after a predetermined volume of gas has been breathed in the rebreathing system in the course of said series of breaths and maintaining it in the open condition until a predetermined volume of gas has been exhaled to the ambient medium.

3. Breathing apparatus as set forth in claim 1, in which the control means include time-independent means for effecting the opening of the rebreathing system for exhalation to the ambient medium automatically after a predetermined number of breaths to and from the rebreathing system have been taken in the course of said series of breaths and maintaining it in the open condition until a predetermined number of exhalations to the ambient medium have been made.

4. Breathing apparatus as set forth in claim 2, in which the control means include means for automatically increasing in dependence of an increase of the ambient pressure the volume of gas breathed in the rebreathing system in the course of said series of breaths.

5. Breathing apparatus as set forth in claim 4, in which the control meansinclude means for maintaining the rebreathing system in the open condition independently of the ambient pressure until a predetermined volume of gas has been exhaled to the ambient medium.

6. Breathing apparatus as set forth in claim 3, in which the control means include means for automatically increasing in dependence of an increase of the ambient pressure the number of breaths of said series of breaths.

7. Breathing apparatus as set forth in claim 6, in which the control means include means for maintaining the rebreathing system in the open condition independently of the ambient pressure until a predetermined number of exhalations to the ambient medium have been made.

8. Breathing apparatus as set forth in claim 1, in which the fresh-gas supply include means for feeding fresh gas having a constant content of oxygen to the rebreathing system.

9. Breathing apparatus as set forth in claim 1, in which the fresh-gas supply includes means for feeding fresh gas having a varying content of oxygen to the rebreathing system.

10. Breathing apparatus as set forth in claim 9, in which the fresh-gas supply includes means for reducing the oxygen content in dependence of an increase of the ambient pressure.

11. Breathing apparatus as claimed in claim 1 wherein said rebreathing system comprises a rebreathing circuit, and said exhalation valve means communicates with said circuit.

12. Breathing apparatus as claimed in claim 11 wherein said exhalation valve means and said control means include means for closing the circuit against circuitous flow of rebreathing gas when the rebreathing system is in open condition with respect to ambient.

l3. Breathing apparatus as claimed in claim 12 wherein said exhalation valve means is located upstream of said means for closing the circuit with respect to the direction of rebreathing flow through the circuit.

14. Breathing apparatus comprising a rebreathing system having exhalation valve means through which exhalation to the ambient medium is possible, a freshgas supply for feeding breathing gas to the rebreathing system to replace breathing gas therein that has been consumed and exhausted to the ambient medium, and control means operating independently of time for maintaining the exhalation valve means of the rebreathing system in closed condition with respect to the ambient medium in the course of a series of breaths to and from the rebreathing system and automatically opening the exhalation valve means of the rebreathing system for exhalation to the ambient medium after the termination of said series of breaths, and thereafter automatically closing the exhalation valve to return the rebreathing system to said closed condition, the exhalation valve means and the control means including two exhalation valves which are biased to closed condition and movable to open condition under the influence of the exhalation pressure, one of these valves being adapted to be opened to open the rebreathing system for exhalation to the ambient medium only while the other one is closed, and integrating means for measuring the volume of gas exhaled to the rebreathing system and including means for blocking said other exhalation valve in its closed condition after a predetermined total volume of gas has been breathed in the rebreathing sys tem in the course of said series of breaths and maintaining it in the closed condition until a predetermined volume of gas has been exhaled to the ambient medium.

15. Breathing apparatus comprising a rebreathing system having exhalation valve means through which exhalation to the ambient medium is possible, a freshgas supply for feeding breathing gas to the rebreathing system to replace breathing gas therein that has been consumed and exhausted to the ambient medium, and control means operating independently of time for maintaining the exhalation valve means of the rebreathing system in closed condition with respect to the ambient medium in the course of a series of breaths to and from the rebreathing system and automatically opening the exhalation valve means of the rebreathing system for exhalation to the ambient medium after the termination of said series of breaths, and thereafter automatically closing the exhalation valve to return the rebreathing system to said closed condition, the exhalation valve means and the controlmeans including two exhalation valves which are biased to closed condition and movable to open condition under the influence of the exhalation pressure, one of these valves being adapted to be opened to open the rebreathing system for exhalation to the ambient medium only while the other one is closed, and a breath counting mechanism including means for blocking said other exhalation valve in its closed condition after a predetermined number of breaths have been taken in the course of said series of breaths and maintaining it in the closed condition until a predetermined number of exhalations to the ambient medium have been made. 

1. Breathing apparatus comprising a rebreathing system having exhalation valve means through which exhalation to the ambient medium is possible, a variable volume storage container in said system for breathing gas, a fresh-gas supply means for feeding fresh breathing gas from said supply directly into the rebreathing system in response to a predetermined reduction of the volume of the storage container to replace breathing gas that has been consumed and exhausted to the ambient medium, and control means operating independently of time for maintaining the exhalation valve means of the rebreathing system in closed condition with respect to the ambient medium in the course of a series of breaths to and from the rebreathing system and automatically opening the exhalation valve means of the rebreathing system for exhalation to the ambient medium after the termination of said series of breaths, and thereafter automatically closing the exhalation valve to return the rebreathing system to said closed condition.
 2. Breathing apparatus as set forth in claim 1, in which the control means include time-independent means for effecting the opening of the rebreathing system for exhalation to the ambient medium automatically after a predetermined volume of gas has been breathed in the rebreathing system in the course of said series of breaths and maintaining it in the open condition until a predetermined volume of gas has been exhaled to the ambient medium.
 3. Breathing apparatus as set forth in claim 1, in which the control means include time-independent means for effecting the opening of the rebreathing system for exhalation to the ambient medium automatically after a predetermined number of breaths to and from the rebreathing system have been taken in the course of said series of breaths and maintaining it in the open condition until a predetermined number of exhalations to the ambient medium have been made.
 4. Breathing apparatus as set forth in claim 2, in which the control means include means for automatically increasing in dependence of an increase of the ambient pressure the volume of gas breathed in the rebreathing system in the course of said series of breaths.
 5. Breathing apparatus as set forth in claim 4, in which the control means include means for maintaining the rebreathing system in the open condition independently of the ambient pressure until a predetermined volume of gas has been exhaled to the ambient medium.
 6. Breathing apparatus as set forth in claim 3, in which the control means include means for automatically increasing in dependence of an increase of the ambient preSsure the number of breaths of said series of breaths.
 7. Breathing apparatus as set forth in claim 6, in which the control means include means for maintaining the rebreathing system in the open condition independently of the ambient pressure until a predetermined number of exhalations to the ambient medium have been made.
 8. Breathing apparatus as set forth in claim 1, in which the fresh-gas supply include means for feeding fresh gas having a constant content of oxygen to the rebreathing system.
 9. Breathing apparatus as set forth in claim 1, in which the fresh-gas supply includes means for feeding fresh gas having a varying content of oxygen to the rebreathing system.
 10. Breathing apparatus as set forth in claim 9, in which the fresh-gas supply includes means for reducing the oxygen content in dependence of an increase of the ambient pressure.
 11. Breathing apparatus as claimed in claim 1 wherein said rebreathing system comprises a rebreathing circuit, and said exhalation valve means communicates with said circuit.
 12. Breathing apparatus as claimed in claim 11 wherein said exhalation valve means and said control means include means for closing the circuit against circuitous flow of rebreathing gas when the rebreathing system is in open condition with respect to ambient.
 13. Breathing apparatus as claimed in claim 12 wherein said exhalation valve means is located upstream of said means for closing the circuit with respect to the direction of rebreathing flow through the circuit.
 14. Breathing apparatus comprising a rebreathing system having exhalation valve means through which exhalation to the ambient medium is possible, a fresh-gas supply for feeding breathing gas to the rebreathing system to replace breathing gas therein that has been consumed and exhausted to the ambient medium, and control means operating independently of time for maintaining the exhalation valve means of the rebreathing system in closed condition with respect to the ambient medium in the course of a series of breaths to and from the rebreathing system and automatically opening the exhalation valve means of the rebreathing system for exhalation to the ambient medium after the termination of said series of breaths, and thereafter automatically closing the exhalation valve to return the rebreathing system to said closed condition, the exhalation valve means and the control means including two exhalation valves which are biased to closed condition and movable to open condition under the influence of the exhalation pressure, one of these valves being adapted to be opened to open the rebreathing system for exhalation to the ambient medium only while the other one is closed, and integrating means for measuring the volume of gas exhaled to the rebreathing system and including means for blocking said other exhalation valve in its closed condition after a predetermined total volume of gas has been breathed in the rebreathing system in the course of said series of breaths and maintaining it in the closed condition until a predetermined volume of gas has been exhaled to the ambient medium.
 15. Breathing apparatus comprising a rebreathing system having exhalation valve means through which exhalation to the ambient medium is possible, a fresh-gas supply for feeding breathing gas to the rebreathing system to replace breathing gas therein that has been consumed and exhausted to the ambient medium, and control means operating independently of time for maintaining the exhalation valve means of the rebreathing system in closed condition with respect to the ambient medium in the course of a series of breaths to and from the rebreathing system and automatically opening the exhalation valve means of the rebreathing system for exhalation to the ambient medium after the termination of said series of breaths, and thereafter automatically closing the exhalation valve to return the rebreathing system to said closed condition, the exhalation valve means and the control means including two exhalation valves Which are biased to closed condition and movable to open condition under the influence of the exhalation pressure, one of these valves being adapted to be opened to open the rebreathing system for exhalation to the ambient medium only while the other one is closed, and a breath counting mechanism including means for blocking said other exhalation valve in its closed condition after a predetermined number of breaths have been taken in the course of said series of breaths and maintaining it in the closed condition until a predetermined number of exhalations to the ambient medium have been made. 